Added simple docs sketch

esp_modem/docs/cxx_api_docs.rst

@@ -0,0 +1,39 @@
+C++ API Documentation
+=====================
+
+Similar to the :ref:`c_api`, the basic application workflow consist of
+
+- Construction of the DCE
+- Sending (AT) commands
+- Switching modes
+- Destroying the DCE
+
+Create DTE and DCE
+------------------
+
+.. doxygengroup:: ESP_MODEM_INIT_DTE
+
+.. doxygengroup:: ESP_MODEM_INIT_DCE
+
+
+Mode switching commands
+-----------------------
+
+.. doxygenclass:: esp_modem::DCE_T
+   :members:
+
+
+Modem commands
+--------------
+
+Create the DCE object with DCE factory :cpp:func:`esp_modem_new`
+
+.. doxygenclass:: DCE
+   :members:
+
+
+Destroy the DCE
+---------------
+
+The DCE object is created as ``std::unique_ptr`` by default and as such doesn't have to be explicitly destroyed.
+It simply gets destroyed and cleaned-up automatically if the object goes out of the block scope.